Abstract: A continuity check tone detector for use with a digital telecommunication system and being designed for detecting continuous tones on voice transmission paths temporarily established between a digital tone generator and the detector across a switching network under control of a switch control unit. The tone detector includes detector interfaces receiving serial tone information from each transmission path in order to derive a digital tone sample and serial control information from the switch control unit in order to convert the same into timing and control signals. A digital signal processor under control of said timing and control signals linearizes and filters received tone samples, measures the power thereof, and supplies corresponding output data. A control processor receives this output data for evaluating the same with respect to individually set power level and predetermined duration for determining the presence of a continuous test tone.